ATP receptors are basically classified into P2X family of ion-channel type receptors and P2Y family of G protein-coupled receptors. Until now, there are reported, respectively, seven sub-types (P2X1-7) and eight sub-types (P2Y1, 2, 4, 6, 11-14).
It has been reported that P2X4 receptor (Genebank No. X87763), which is a sub-type of P2X family, is present widely in the central nervous systems. See the following documents:    Non-patent document 1: Buell, et al. (1996) EMBO J. 15: 55-62;    Non-patent document 2: Seguela, et al. (1996) J. Neurosci. 16: 448-455;    Non-patent document 3: Bo, et al. (1995) FEBS Lett. 375: 129-133;    Non-patent document 4: Soto, et al. (1996) Proc. Natl. Acad. Sci. USA 93: 3684-3788; and    Non-patent document 5: Wang, et al. (1996) Biochem. Res. Commun. 220: 196-202.
The mechanism of pathogenesis of intractable pains such as neuropathic pain is unclear. Therefore, if non-steroidal anti-inflammatory drugs (NSAIDs) and morphine are not effective, there is no other pharmacotherapy. In that case, the patient and surrounding people take up a heavy burden in mind and body. The neuropathic pain is caused by injury of peripheral or central nervous systems, for instance, post-surgery pain, cancer, spinal cord injury, herpes zoster, diabetic neuritis, or trigeminal neuralgia.
Recently, Inoue, et al. studied the involvement of P2X receptors in neuropathic pain using dorsal root ganglion neuron-injured animal model which induces allodynia, and indicated that the nerve-injured pain (particularly, allodynia) is caused via P2X4 receptors on spinal microglia. See the following documents:    Non-patent document 6: M. Tsuda, et al. (2003) Nature, 424, 778-783;    Non-patent document 7: Jeffrey A. M. Coull, et al. (2005) Nature, 438, 1017-1021; and    Patent document 1: United States patent publication No. 20050074819.
Accordingly, compounds that inhibit the action of P2X4 receptors are expected to be employed for preventing or treating nociceptive, inflammatory, and neuropathic pains.
WO 2004/085440 (Patent document 2) discloses that benzofuro-1,4-diazepin-2-one derivatives having the below-illustrated formula (A) show P2X4 receptor antagonism:
wherein R1 is halogen, and R2 is hydrogen, halogen, nitro, cyano, C(O)—OR3, C(O)—NR4R5, SO2—OR3, or SO2—NR4R5, or in which R1 is hydrogen, and R2 is halogen, nitro, cyano, C(O)—OR3, C(O)—NR4R5, SO2—OR3, or SO2—NR4R5.
The present inventors have found 1,4-diazepin-2-on derivatives showing P2X4 receptor antagonism, and filed the following patent applications:    Patent document 3: WO 2007/072974    Patent document 4: WO 2007/074940    Patent document 5: WO 2008/023847    Japanese Patent Publication No. 2 (1990)-30443 (Patent document 6) discloses compounds represented by the following formula (C):

Patent document 6 describes that the compounds represented by the formula (C) can be used as photographic couplers. Patent document 6, however, is silent with respect to the relation between these compounds and the P2X4 receptor antagonism.